Geometric Correction

Nathan Sylte
Lab 6

Geometric Correction

Goals and Background:  

    Lab six involved the introduction to geometric correction, which is extremely important in image processing. Specifically, lab six is designed to better ones abilities on image to map rectification, as well as image to image registration. Both of these processes are important in geometric correction and are often required to maximize data extraction from satellite images.

    There were two parts to lab six. Part one involved image to map rectification. In this case, a digital raster graphic (DRG) of the Chicago Metropolitan Area was used to correct a Landsat TM image of the same area. Part two involved image to image registration of an image of the Sierra Leone region.

Methods:

    To achieve the image correction of the Landsat TM image of Chicago, two images were brought into two separate viewers. The two images included the Landsat Chicago image as well as a reference image of the same area. The Landsat image served as the input image. The control points tool was selected and the polynomial geometric model was used. Specifically, the first order polynomial model was used. Four ground control points were then added to both the reference image and the input image with a control point error of less than two percent. The image below shows the ground control points used in part one of the lab.

 Figure 1. Figure one shows the Chicago Metropolitan Area, and the ground control point locations for part one of the lab. The image on the left of the frame is the reference image.

    Image correction of the Sierra Leone satellite image involved a similar process. The control points tool was used again; however, this time the third order polynomial model was used. Twelve control points were selected. For resample methods, the method was changed from nearest neighbor to bilinear interpolation. After the processes were complete, the new corrected images were compared to their reference images to look at spatial accuracy. The figure below shows the ground control points used in part two of the lab.

Figure 2. Figure two shows the Sierra Leone region, and the ground control point locations for part two of the lab The image on the left is the reference image.  

Results:

    Below is the result from part one.

Figure 3. Figure three shows the geometrically corrected image of the Chicago Metropolitan Area.

    Below is the result from part two.

Figure 4. Figure four shows the geometrically corrected image of the Sierra Leone region.

Sources: All images are from the Earth Resources Observation and Science Center, United States Geological Survey.

Geological Survey

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Geological Survey

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United States Geological Survey. (n.d.). Earth Resources Observation and Science Center. Retrieved from http://eros.usgs.gov/